Not quite. Suppose two people reply to my node here. I might want to reply to both of them, and I'm too lazy to change their node titles to be different. The submission system you propose would not allow that.
I agree it might be nice to have a system in place for refusing duplicate nodes, but I don't think this is the way to do it. Right now, moderators can submit a node "for consideration", meaning duplicates that need deleting, etc. Very few people make this mistake twice; maybe all that's needed is to improve the message text in a few places to make it clear what's happening when you post a node.
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